The metabolism of methylamine by the nonphotosynthetic bacterium Pseudomonas sp. (Shaw strain MA) involves the conversion of methylamine to formaldehyde, followed by the condensation of formaldehyde with glycine to yield serine. For carbon assimilation, glycine is regenerated in a cyclic process involving phosphoenolpyruvate and malate thiokinase as key reactions, with 3 phosphoglycerate as the final product. The assimilatory process is an energy consuming one, and cannot account for cell growth. The phosphoenolpyruvate carboxylas reaction is activated by NADH and inhibited by ADP, thus indicating the activity of this enzyme, reflects the energy state of the cell. When the cell is in need of energy, the NADH concentration is low, the ADP concentration high, and phosphoenolpyruvate is not acted upon by phosphoenolpyruvate carboxylase, but instead by pyruvate kinase. The reaction with this enzyme leads to a net synthesis of ATP and the complete oxidation of methylamine. On the other hand, when there is sufficient energy for the cell, the NADH concentration is high, the ADP concentration low, and phosphoenolpyruvate is carboxylated via the phosphoenolpyruvate carboxylase reaction and commits the flow of carbon assimilation. Thus, the phosphoenolpyruvate carboxylase reaction serves as a key control point between energy metabolism and carbon assimilation.